The present invention relates to a large-sized container excellent in the impact resistance, solvent permeation resistance and moldability.
For containers used for solvents and the like, metal- or glass-made containers have been commonly used so far, but, recently, plastic-made containers have come into use. The plastic containers have various merits of light weight, excellent impact resistance, unnecessity of treatments such as rust-proofing etc., high freedom in design, and the like. As a plastic satisfying these features, polyolefins are suitable from their excellent processibility and is utilized in different fields such as containers for various industrial chemicals, kerosene cans, drum cans, gasoline tanks, and the like.
However, as a drawback of polyolefin containers, poor solvent permeation resistance can be mentioned. In order to improve this drawback, there is a multilayer container of laminated polyolefin with a barrier resin such as polyamide or the like. But, from the fact that polyamide has no affinity to polyolefin, an adhesive layer must be interposed between both layers at the time of lamination.
For this reason, there have been in dangers that, in the case of a large-sized container, peeling-off occurs between layers caused by a large impact upon dropping because of the large inner volume thereof and the wall thickness becomes nonuniform by the draw-down of parison on blow molding thereby increasing the impact resistance. Moreover, the adhesion strength sometimes decreases at those portions of thin wall thickness originating from the nonuniformity of wall thickness. Hence, higher adhesion strength is required in the case of a large-sized container over the case of a small-sized container.
On the other hand, in the case of containers for solvents such as alcohol etc., polyamide tends to swell with alcohol etc. Hence, the case that the polyamide layer cannot be used for the inner layer of container has often been experienced. Moreover, it could not be used for the outer layer due to the problem of impact resistance. Thus, polyamide is positioned as the intermediate layer, but, in this case, the construction of the container cannot help becoming a complicated construction comprising three kinds of materials and five layers of polyolefin/adhesive/polyamide/adhesive/polyolefin. According to the method of making the construction with three kinds and five layers, a complicated structure of dies is required as well as the necessity of at least three extruders resulting in very complicated installation and production.
The objective of the invention is to provide a large-sized container wherein, different from the case of such conventional method, the adhesion is good without the interposition of an adhesive layer and yet the processibility and the impact resistance are good.
As a result of diligent investigations in view of the situation aforementioned, the inventors have found a large-sized container of two kinds of materials and three layers not requiring the adhesive layer, leading to the completion of the invention.